Conventionally, there is known a drive assisting system for carrying out a drive assisting according to driving characteristics of a driver who drives a vehicle. For example, Patent Literature 1 described below discloses a device for warning a driver of a driver's own vehicle to carry out a brake operation to prevent a collision with a target such as a preceding vehicle from back and a technology for adjusting timing of issue of a rear end collision warning, i.e. a relative distance (warning distance) to the target to which the rear end collision warning is issued. The warning distance is adjusted based on a speed of a driver's own vehicle at the time of brake operation of the driver to the target and on a relative speed of the target to the driver's own vehicle.
Note that, Patent Literature 2 described below discloses a technology for calculating a perceived relative distance between a driver's own vehicle and a perceived target based on an actual relative distance between the driver's own vehicle and the perceived target, a technology for calculating a perceived relative speed between the driver's own vehicle and the perceived target based on an actual relative speed between the driver's own vehicle and the perceived target, and a technology for calculating a ratio (perceived relative ratio) between the perceived relative distance and the perceived relative speed and carrying out a vehicle control when the perceived relative ratio exceeds a threshold value. The perceived target is an object recognized by the perception of a driver in driving operation. The perceived relative distance is a relative distance to a perceived target recognized by the driver. The perceived relative speed is a relative speed to the perceived target recognized by the driver. Further, Patent Literature 3 described below discloses a technology that a history of brake operation timings and steering operation timings by a driver when a relative distance between a driver's own vehicle and a preceding vehicle has become a predetermined distance are stored and average values of the respective timings are calculated, when a relative speed to the preceding vehicle is equal to or less than a predetermined value, a warning is issued by comparing an actual numerical value of the driver as to the brake operation timing with the average values, and when the relative speed to the preceding vehicle is larger than the predetermined value, a warning is issued by comparing an actual numerical value of the driver as to the steering operation timing with the average values.